The present invention relates to a method for detecting a modulated video signals, and more particularly for a method for detecting the presence of an auxiliary signal within a modulated video signal for signaling purposes.
Various methods exist in the art for transmitting an auxiliary signal along with video signals, wherein the auxiliary signal is used for a variety of signaling purposes. Several of these methods transmit the auxiliary signal in the video signals by replacing active portions of the video signal with auxiliary data, such that users who view the video signal on their display devices (e.g., televisions) will see the effect of the auxiliary signal in the form of an icon, dot or other visual image or disturbance in the picture. Other methods transmit auxiliary signals in non-viewable scan lines of the video signal, such as in the vertical blanking interval (VBI). However, these scan lines may already contain other auxiliary signals such as signals that represent cueing information, timing information or closed captioning information and are prone to being stripped by programming operators prior to broadcast.
Another method for transmitting an auxiliary signal in video signals is described in U.S. Pat. No. 4,807,031 to Broughton et al. (“Broughton”) entitled “Interactive Video Method and Apparatus”, which relates generally to in-band video broadcasting of commands and other encoded information to interactive devices and is incorporated by reference herein. The invention described therein relates generally to interactive educational and entertainment systems, and is described in one embodiment in the context of television program control of toys located where there is a television receiver, as within a residence.
To encode control data, Broughton discloses a novel method of luminance or chrominance modulation of a video signal that creates a composite video signal, wherein the video signal is modulated with control data. The novel modulation method alternately raises and lowers the luminance/chrominance of paired adjacent horizontal scan lines to create a video subcarrier that contains the control data.
In Broughton, the video signal is not being replaced with other data, nor is the data being added as a separate signal along with the video signal. Rather, the video signal itself is modulated to carry the control data. Therefore, the control data is a part of, or contained within, the video signal and yet is imperceptible to the human eye and relatively invisible. The encoding method also includes preview and remove circuitry to ensure suitability or the presence of data encoding and removal of data encoding, respectively.
The control data is transmitted either by television broadcast means, or by pre-recorded video players that are connected to a video display. The control data is then received by the video display where at least one video field of the video display is modulated by control data. The control data is then detected with either opto-electronic or radio frequency (RF) detection means that discriminate between the program material and the control data to detect the control data. The detected control data is further reproduced so that the control data can be used with an interactive device.
Improvements on the method of modulation described in Broughton are described in U.S. Pat. No. 6,094,228 to Ciardullo et al. and U.S. Pat. No. 6,229,572 to Ciardullo et al. (referred to collectively herein as “Ciardullo”). Both Ciardullo patents describe improved methods of modulation wherein the auxiliary data is inserted on the visual portion of a video signal by changing the luminance of paired scan lines in opposite directions. Instead of raising and lowering the intensity on the whole line as in Broughton, Ciardullo uses pseudo noise sequences to raise and lower the intensity on portions of a first line, where the line paired to the first line is modulated with the inverse pseudo noise sequences. Ciardullo thereby allows larger amounts of auxiliary data to be modulated in the video signal by use of the pseudo noise sequences. Broughton and Ciardullo, which are owned by the assignee of the present invention, are incorporated by reference herein.
Still another patent application by the assignees of the present invention is U.S. patent application entitled “Method and Apparatus for Modulating a Video Signal With Data”, Ser. No. 10/676,940, filed on Oct. 1, 2003, of Yousri H. Barsoum, Alan G. Maltagliati, Daniel A. Ciardullo and Christopher E. Chupp (the application being herein referred to as “Barsoum”), which is incorporated by reference herein. Barsoum describes the use of a memory card coupled to a slotted hand-held device for receiving video signals modulated with carrier signals by use of the memory card, transmitting the signals from the card to the slotted hand-held device, detecting the carrier signals or decoding auxiliary data from the video signals on the slotted hand-held device and providing the user of the slotted hand-held device with a benefit from the detection of the carrier signals and/or the reception of the auxiliary data. Barsoum also describes a method of improving the reliability and speed of the transmission and reception of auxiliary data by storing data in video frames split into multiple regions and encoding complementary data bits in each region.
Still another patent application by the assignees of the present invention is U.S. patent application entitled “Method And System of Detecting Signal Presence from a Video Signal Presented on a Digital Display Device”, Ser. No. 10/817,109, filed on Apr. 2, 2004, of James G. Withers, Yousri H. Barsoum, Edward J. Koplar and Michael C. Reynolds (the application being herein termed “Withers II”), which is incorporated by reference herein. Withers II describes several methods and apparatus for modulating video signals with signal presence and signal absence for use on digital display devices.
Yet another patent application by the assignees of the present invention is U.S. patent application entitled “Method and System for Enhanced Modulation of Video Signals”, Ser. No. 10/888,919, filed on Jul. 9, 2004, of Christopher E. Chupp, Michael S. Gramelspacher, Jesse J. Chounard II, James G. Withers, Yousri H. Barsoum and Michael C. Reynolds (the application being herein termed “Chupp”), which is incorporated by reference herein. Chupp describes a method and apparatus for determining an optimum level and placement of a carrier signal (i.e., an auxiliary signal) to be modulated into an active portion of a video signal so as to deter nefarious third parties from stripping the carrier signal out of the video signal and increase the detectability of the carrier signal within the video signal without noticeably decreasing the clarity of a picture represented by video signal to a viewer.
Yet another application by the assignees of the present invention is U.S. Utility Patent Application entitled “Methods for Improved Modulation of Video Signals”, Ser. No. 10/958,865 filed on Oct. 4, 2004, of Michael C. Reynolds, James G. Withers, Yousri H. Barsoum, Jesse J. Chounard II and Edward J. Koplar (the application being herein termed “Reynolds”), which is incorporated by reference herein. Reynolds discloses optical improvements for increasing the detectability and reducing the visibility of carrier signals.
At the time of the present invention, analog display devices (e.g., NTSC televisions) operate by use of a fine pitch electron beam that strikes phosphors coating on an internal face of the cathode ray tube (CRT). The phosphors emit light of an intensity which is a function of the intensity of the beam striking it. A period of 1/60 second is required for the electron beam to completely scan down the CRT face to display a field of the image. During the following 1/60 second, an interlaced field is scanned, and a complete frame of video is then visible on the analog display device. The phosphors coating on the face of the tube is chemically treated to retain its light emitting properties for a short duration. Thus, the first area of the scanned picture begins to fade just as the electron beam retraces (i.e., during the vertical retrace) to the top of the screen to refresh it. Since the electron beam covers 525 lines 30 times per second, a total of 15,750 lines per second is viewed each second.
The Broughton method of modulating video signals to create an auxiliary signal and its improvements were generally intended for use with analog display devices. The Broughton method relies on the interlaced scanning process during video signal transmission. Upon receiving the video signal from the signal source, the display device splits the video signal into sequentially transmitted images referred to as frames, whereby each frame of an NTSC television image has 525 horizontal scan lines. The display device scans 262.5 of the horizontal lines left to right and top to bottom by skipping every other line, thus completing the scan of a first field, and then retracing to the top of the image and scanning the remaining 262.5 lines, for a second field. The fields are interlaced at the display device and construct one complete frame. When the video signal is broadcast at 525 lines per frame and 30 frames a second there are 60 fields per second and a line frequency rate (i.e., the speed at which lines are refreshed) of 15,750 Hz (i.e., approximately 16 kHz).
The use of Broughton and other methods of modulating video signals to contain an auxiliary signal may be undesirable in embodiments where the broadcast source is from a computer. When video signals are digitally encoded in a video file or stream and are played back by use of a computer, the scan lines of a first field of a frame of the video signal may become blended with the video scan lines of a second field of the frame such that the auxiliary signal in the first field is smeared between the two fields. If the intensity of the second field is used as a reference with the intensity of the first field, a comparison of the two may return erroneous results.
There is a need in the art for a system that selectively increases and decreases the intensity of video scan lines in a plurality of fields of a video signal over a time interval and does not increase or decrease the intensity of the video scan lines in the remaining plurality of fields, thereby enabling a decoder to use an average intensity value of the nonencoded fields as a reference with the average intensity value of the encoded fields, or to accumulate the differences in signal strength when fields are changing state from encoded to unencoded or encoded to unencoded to determine whether an auxiliary signal is present during the time interval.